Network Working Group J. Snell
Internet-Draft March 28, 2007
Intended status: Standards Track
Expires: September 29, 2007
Atom License Extensiondraft-snell-atompub-feed-license-11.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This memo defines an extension to the Atom Syndication Format for
describing licenses associated with Atom feeds and entries.
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Internet-Draft Feed License March 20071. Introduction
This document defines an extension to the Atom Syndication Format
that can be used to add links to Atom feed or entry documents
referencing resources that describe the explicit rights that have
been granted to consumers of those documents.
Describing licenses using the mechanisms defined in this
specification is currently considered to be largely experimental.
While it is a common practice for feed publishers to associate
licenses with syndicated content, there are still very few feed
consumers that utilize such metadata and the effectiveness of doing
so is still largely unknown. As it is not yet certain how these
mechanisms will be used, implementations and feedback are encouraged.
1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, [RFC2119].
1.2. Terminology
The term "link relation" refers to the value of the Atom link
elements "rel" attribute as defined in section 4.2.7.2 of [RFC4287].
The term "license" refers to a potentially machine-readable
description of explicit rights that have been granted to consumers of
an Atom feed or entry. Rights granted by a license may be associated
with obligations which must be assumed by those exercising those
rights.
Atom allows the use of IRIs [RFC3987]. Every URI [RFC3986] is also
an IRI, so a URI may be used wherever below an IRI is named. When an
IRI that is not also a URI is given for dereferencing, it MUST be
mapped to a URI using the steps in Section 3.1 of [RFC3987].
Atom allows the use of the xml:base attribute
[W3C.REC-xmlbase-20010627] to establish the base URI (or IRI) used to
resolve any relative references as described in section 5.1.1 of
[RFC3986].
Atom allows the use of the xml:lang attribute to indicate the natural
language of an element, its attributes and its descendents. The
language context is only significant for elements and attributes
declared to be "Language-Sensitive" as described in [RFC4287]. The
title attribute of the atom:link element is defined as being
Language-Sensitive.
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Internet-Draft Feed License March 20072. The "license" link relation
The "license" link relation can be used to associate licenses with a
feed or entry.
Feed and entry elements MAY contain any number of "license" link
relations but MUST NOT contain more than one with the same
combination of href and type attribute values. The IRI specified by
the link's 'href' attribute SHOULD be dereferenceable to return a
representation of the license. The license representation MAY be
machine readable.
Feeds and entries can be dual-licensed by including multiple
"license" link relations specifying different href attribute values.
If multiple license link relations are specified, each SHOULD contain
a title attribute specifying a human-readable label for the license.
2.1. Unspecified License Links
A publisher can use an "unspecified license link" (a "license" link
relation with an href attribute value equal to
"http://purl.org/atompub/license#unspecified") to indicate that a
feed or license has not been explicitly linked to a license
description.
A feed or entry containing an unspecified license link MUST NOT
contain any other license link relations.
2.2. Comparing License Links
Atom implementations that are capable of supporting license links
SHOULD use the simple string comparison method described in [RFC3987]
Section 5.3.1 to determine whether multiple license links are
equivalent. The other comparison methods discussed in Section 5.1 of
the IRI specification MAY be used. If the license link is specified
using a relative reference, it MUST be converted to it's fully
qualified form before comparison.
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Internet-Draft Feed License March 20072.3. Example
<feed xmlns="http://www.w3.org/2005/Atom">
<id>http://www.example.com/myfeed</id>
<title>My Example Feed</title>
<updated>2005-07-28T12:00:00Z</updated>
<link href="http://www.example.com/myfeed" />
<link rel="license" type="application/rdf+xml"
href="http://creativecommons.org/licenses/by-nc/2.5/rdf" />
<rights>
Copyright (c) 2005. Some rights reserved. This feed
is licensed under a Creative Commons Attribute-NonCommercial
Use License. It contains material originally published by
Jane Smith at http://www.example.com/entries/1 under the
Creative Commons Attribute License.
</rights>
<author><name>James</name></author>
<entry>
<id>tag:entries.org,2005:1</td>
<title>Atom Powered Robots Run Amok</title>
<updated>2005-06-28T12:00:00Z</updated>
<link href="http://www.example.org/entries/1" />
<summary>Atom Powered Robots Run Amok</summary>
<author><name>Jane Smith</name></author>
<link rel="license" type="text/html"
href="http://creativecommons.org/licenses/by/2.5/" />
</entry>
</feed>
2.4. Inherited Licenses
License links specified within atom:feed or atom:source elements are
inherited by entries. Generally, a more specific license overrides a
less specific license. More specifically, if an atom:entry has any
license link relations, including the "undefined" license, it does
not inherit any license from a containing atom:feed element or
contained atom:source element. If an entry as no license link
relations, and contains an atom:source element, it inherits licenses
from the atom:source. If the atom:source element contains no license
links, or if the entry does not have an atom:source element, the
entry inherits licenses from the containing atom:feed.
An entries license MAY be inherited by media resources associated
with the entry. Some media types have ways of including license
information, which always overrides the entry's licensing.
An agent searching to find entries that fall under a specific license
(e.g. search for entries containing pictures and the word "knitting"
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Internet-Draft Feed License March 2007
where the entry is under any Creative Commons license) MUST check the
most granular license definition available, rather than assume
license inheritance without checking.
2.5. Relationship with the "atom:rights" element
License link relations are related to the "atom:rights" element in
that both are intended to communicate information about the rights
associated with an Atom document. Where the two differ, however, is
in the fact that "atom:rights" is intended strictly as a human-
readable assertion of rights held over a work while the license link
relation is intended to provide a potentially machine-readable
description of what rights have been granted to others. The two
constructs may overlap one another and conflicts could arise if they
are contradictory. It is important that publishers of Atom documents
ensure that the "atom:rights" and license link relations are
consistent with one another.
If an atom:entry which does not contain an atom:source is copied from
one feed into another feed then if the feed into which it is copied
contains a license, an atom:source element SHOULD be added to the
copied entry. If a source feed contains a license, that license
SHOULD be preserved in an atom:source element added to any entries
copied from the source feed which do not already contain atom:source
elements.
3. Security Considerations
When "license" link relations are used in Atom documents, the
security considerations specified in [RFC4287] Section 8 apply.
4. IANA Considerations
This specification defines one new Atom link relation type to be
registered in the IANA Registry of Link Relations as defined by
[RFC4287].
Attribute Value: license
Description: Specifies the IRI of a license associated with
the containing feed, entry or source element.
Expected display characteristics: None
Security considerations: When "license" link relations are used
in Atom documents, the security considerations for
handling links in Atom documents apply.
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Internet-Draft Feed License March 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
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Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Snell Expires September 29, 2007 [Page 8]